As is well known to those versed in the venetian blind art, under certain circumstances it is desired to provide venetian blinds which may be locked upon elevation of the slat assembly to its uppermost position. By this means, apartment houses, office buildings and other similar large buildings are rendered more attractive from the outside, as the haphazard appearance of venetian blinds at a multitude of different slat settings or elevations is avoided.
However, prior art blind assemblies having automatic top position locking have been relatively complex in structure and consequently unreliable in operation, requiring considerable maintenance to assure satisfactory operability.